Radio signaling system



Feb. 17, 1931.

G. T. ROYDEN RADIO SIGNALING SYSTEM Filed Dec. 22, 1926 5 Sheets-Sheet l Feb. 17, 193]. T, RQYDEN 1,793,016

RADIO SIGNALING SYSTEM Jinn:

w ITTORNEYS Feb. 17,1931. T, Y E 1,793,016

RADIO SIGNALING SYSTEM Filed Dec. 22 1926 I5 Sheets-Sheet 3 FIE- 4;-

ig/MW fl TTURIIEYS Patented Feb. 17, 1931 UNITED STATES PATENT lorries GEORGE '1'. ROYDEN, OF PALO ALTO, CALIFORNIA, ASSIGNOR T FEDERAL TELEGRAIH COMPANY, OF SAN FRANCISCO, CALIFORNIA, A GORPORA'I'ION 0]! CALIFORNIA namo SIGNALING sysrnm .applilsat ion filed December 22, 1926. Serial No. 156,309.

This invention relates generally to radio signaling or other amplifying systems adapted to be energized from a source of alternating current.

In operating radio receiving sets from alternating current, difficulty is experienced not only in suppressing the alternating current ripple but also in obtaining an undistorted response when used for telephon c reception.- Even though the transformers coupling togetherthe amplifiers are designedto amplify uniformly over the ent re voice range, the system will frequently distort the low tones and cause rumbling noises in the loud speaker. I have found that much of this distortion is caused by interaction between the different amplifier stages through the common source of current supply. Former types of alternating current supply systerns have also been expensivebecause of the necessity of elaborate filters to minimize current fluctuations.

It is an object of this invention to devise a radio signaling system for operation from 2 alternating current in which interaction'between the amplifier stages will be minimized.

It is a further object of this invention to devise a novel means for supplying a negative potential to the grid of an amplifier tube which is being energized from a source of rectified alternating current.

It is another object of this invention to minimize noises produced in alternating current radio signaling systems because of fluctuations in the wave form of the alternating current supply.

It is a further object of this invention to reduce the cost of and simplify the construction of filters for rectified alternating current by utilizing the field inductance of a' loud speaker or other translator as one element of the filter. i

Further objects of this invention will appear from the following description in which I have set forth the preferred embodiment of my invention. It is to be understood that the claims are to be accorded a range of electrical equivalents consistentwith the state of the prior art. 50 Referring to the drawings:

eliminator incorporating the field inductance of a loud speaker as one element of a filter circuit.

The invention has been illustrated in the drawing as being combined with a conventional form of radio receiving apparatus, although it is to be understood thatcertain features are applicable to a variety of systems employing electron emission relays. The particular apparatus which I have shown comprises 'a plurality of electron relays coupled together in cascade so as toform a high frequency amplifier, a low frequency amplifier for actuating a translator or loud speaker, and an intermediate detector, modulator or integrating device. Although any number of stages of amplification may be employed,' the circuit has been simplified by showing only one stageof high or radio frequency amplificationformed by the electron relay 11. The output of the relay 11 is coupled to the input of the detector relay 12 while the output of the detector supplies one or more stages of low or audio frequency amplifiers indicated diagrammatically at 13.

The last stage of audiofrequency amplification is preferably formed by a power amplifier relay 14, the output of which supplies a translator or loud speaker 15. These electron relays are preferably of the three-element. type comprising a grid'or control element 17 electron emission clement-or filament 18, and plate or anode 19. Asis well known in the art, the input circuit of each relay is connected across the grid 17 and electron emission element 18, while the output circuit is connected across the plate 19 and electron emission element. The firstamplifier stage a is coupled to a suitable source of signal 100 a to the ositive anode potential energy such as an antenna 21 and ground 22, as by means of a tuned coupling transformer 23. The output of the electron relay 11 is similarly coupled to the input of detector tube 12 by means of a tuned radio frequency transformer 24, the output of the detector is coupled to the amplifier 13 by means of an audio frequency transformer 26, and the output of this amplifier coupled to the power amplifier sta e 14 by means of audio frequency transformer 27.

The filaments of all of the relays with the exception of the power amplifier relay, are preferably connected in series relation across the bus conductors 101 and 102 which are adapted to be connected to a supply of direct current. The filament of the power amplifier 14 is preferably connected to a source of alternating current through bus conductors 103 and 104. The filaments of all the various electron relays are grounded to the negative B battery conductor 106. The outputs of the different electron relays are energized from a source of current which may be arranged to su ply different potentials to the tubes depen ing upon their function. For example, the output of amplifier tube 11 and the outputs of the relays comprising amplifier 13, are-shown as connected to a common anode potential bus conductor 107 which is adapted to su ply a potential of say from 45 to 100 v0 ts. For supplying current at a lower potential to the detector relay 12, the output of this relay is connected us conductor 108. I s the ower amplifier 14 requires a relatively hi h anode potential, the output circuit of re ay 14 is connected to the us conductor 109. In order to maintain the proper negative bias upon the grids of the amplifier relays the potential drop across the series filaments may be employed or there may be provided a grid bias bus conductor 110 with which the inputs of amplifier relay 11 and the relays of amplifier 13 may be associated. A potentiometer 29 may be employed for varying the ne 'ative bias upon the grid of relay 11. As the power amplifier relay 14 requires a much higher negative grid bias a separate anode bus conductor 111 is associated with the input circuit of this relay.

While any standard form of loud s eaker or translator may be employed, I pref rably em loy one having a wound field coil adapted to e energized from a source of direct current. Thus in the loud speaker indicated there is provided an exciting coil 31 connected in the output circuit of power amplifier relay 14, and a field coil 32 having arelatively high inductance. For a purpose later to be described one terminal of field coil 32 is connected to bus conductor 112 while the other terminal is connected to bus conductor 101.

In Fig. 2 there is shown a system adapted to be connected to alternating current supply lines for the purpose of sup ly current to the various bus conductors o the apparatus described with reference to Fi 1. This system includes a transformer 3611M- ing its primary winding 37 connected to the alternating current power supply lines L and L, which may be ordinary 6O cycle 110 volt lighting circuit. This transformer is provided with a plurality of secondary windings for supplyin alternating current at different voltages. Thus the secondary windin 38 serves as a source of anode potential an has its central ta ggunectcd with tl ie negative bus conductor 6.

As it is desirable from the standpoint of efiiciency to employ full wave rectification,

each terminal of winding'38 is connected to one or more rectifier elements, the number of elements employed depending upon the amount of current required. These rectifier elements may be of any common type such as electrolytic, electrochemical, or electronic. In this particular system I have incorporated the use of electronic rectifiers having filamentary cathodes. For energizing the filaments of the rectifier elements the low voltage transformer windings 43 and 44 are provided.

The rectifier elements are arranged in two separate groups, one oup for supplying the anode potential an the other group for supplying the current for energizing the file-- ments of the electron relays. For example, the elements 40 have their. filaments connected to the wires 46and 47 from the trans former winding 43 and form one group of rectifier elements for supplying the anode potential, while the other rectifier elements 41 have their filaments connected to wires 48 and 49 leading from the transformer winding 44 and form the other group of rectifier elements for supplying the filament current. A positive connection to the rectifier circuit is made through wire 51 which is tapped to an intermediate point of transformer winding 43. The corresponding negative wire 52 is connected tothe central tap 39 of transformer winding 38 through the resistances 53 and 54 or other impedances having substantial values of resistance, these resistances being for a purpose later to be described. Interposed between the terminal wires 51 and 52 and the anode bus conductors are separate filter circuits 56 and 57. Filter circuit 56 for example may comprise a plurality of inductive elements or choke coils 58 connected in series relation, to the intermediate points of which are connected the shunt capacitances 59. The filter circuit 57, since it serves to supply the power amplifier, consists merely of a single choke or inductive element 61 and a capacitative element 62. While the filter circuits 56 and 57 have been 39 indirectly electrically be further shunted by capacitance 66 in order to utilize impedance 64 as a filter element.

The current for suppl ing the filaments of the electron relays is ta en through wire 67 which is tapped in at an intermediate point of transformer winding 44, and wire 68 which is connected to intermediate tap 39 of winding 38 either directly thereto or in series with resistances 53 and 54. A suitable form of filter circuit 69 is interposed between wires 67 and 68 and the bus conductors 202 and 212. One form of satisfactory filter comprises a resonant circuit 71 inserted in series with positive wlre 67, this circuit comprislng a capacitance shunted across an inductance and being tuned to reject the second harmonic of the alternating current frequency, this harmonic bein 120 c cles in case of a 60 cycle supply he ot er parts of the filter include inductive elements or chokes 72, between which are connected the shunt ca 'acitances 7 3-. A resonant circuit inclu ing inductance 74 and series capacitance 75 is shunted across wires 67 and 68 and tuned to admit the second harmonic of the alternating current frequency. The filament bus conductor 201 is connected to the negative conductor 202 through series capacitance 76. Instead of supplying direct current to. the filament of the power amplifier relay, this filament is supplied with alternating current from the transformer winding 77 the terminals .of which are connected to bus conductors 203 and 204. The central point of transformer winding 77 .is preferably grounded to wire 68 by means of wire 7 8.

To provide the necessary negative grid/bias upon the amplifier relays, it has previously been the practice to either employ a separate 0 battery or to utilize the potential drop across the relay filaments. Although this method may be satisfactory for the high frequency amplifiers and for the first stages of the low frequency amplifiers, it is impractical for the power amplifier relay since devices of this kind require a relatively high bias in excess of a potential drop across the relay filament. Furthermore, it is usually desirable as disclosed in the above system,.' to energize the filament of the power amplifier relay with alternating current because of its relatively heavy current consumption. To obviate the use of 'a large C battery, I have provided means for securing the necessary negative potential from the rectifier circuit.

Thus a drop in potential is produced between the intermediate tap 39 of transformer winding 38 and either one or both of the negative conductors or filters 56 and 69 by inserting series resistances 53 and.54. The drop across resistance 54 is im osed upon bus conductor 210 while the com bined drop across resistances 53 and 54 .is imposed upon bus conductor 211. The impedance of these resistances may be sufiicientto minimize the ri ples of rectified alternating current as su stantially no current flow will occur through conductors 210 or 211. However, additional filter means is preferably provided as by the use of resistance 79 inserted in series with conductor 211 and wire 39, and shunt capacitance 81. If desired, any or all of resistances 53, 54 and 79 may be replaced by choke coils. The use of a filter circuit between the source of rid bias potential and the input circuits of. the relays is of value in minimizing distortion. It frequently happens that the power relay is loaded to capacity or even overloaded, so that at times the anode filter circuit must deliver a relatively heavy current. As the potential drop across resistances 53 and 54 is dependent upon current flow, the bias upon the grid may be unduly disturbed, thus causing a distorted output. Distortion from this cause is most noticeable when am lifying voice currents of low frequency. owever, by inserting the filter circuit described above these variations on the grid are minimized and the relay faithfully repeats input current modulations within a broad range of loadings and .frequencies.

Because of the cascade arrangement of the electron relays very slight fluctuations in the energizin current for the high frequency stages wi 1 cause greatly amplified noises in the loud speaker. Even if the rectified alternating current is completely filtered to minimize substantially all alternating current ripple, such interfering noises may still be produced by sudden fluctuations upon the alternating current supply lines due to the opening and closing of other circuits associated with the same. For example, with a radio receiving set installed in a dwelling, the operation of a lighting switch or a small motor from the same alternating current lines will cause sudden surges in the transformer 36, and as it is practically impossible to successfully filter out all of these surges after being rectified, interfering noises will be set up in the loud speaker. As one feature of this invention I propose to minimize noises produced by sudden surges upon the alternating current lines by imposing a filter circuit between the supply lines and the transformer 36, the filter circuit being in proximity to the transformer. Thus as shown in Fig. 2, such a filter circuit may comprise series inductances or chokes 82 and shunt capacitances 83. By means of this filter sudden surges in the line at a point remote from the filter will not be transmitted to the secondary windings of the transformer.

In operating the above system, by virtue of the fact that field coil 32 of the loud speaker 15 is connected across bus conductors 201 and 212, this coil will be incorporated as one reactive element of the filter circuit69. Atthe same time that the coil 32 is serving as a filter element, it is also being energized by the same source of current serving to energize the filament of the relay. By utilizing the field coil of the loud speaker in this manner, a less number of chokes may be employed in the filter circuit 69 with the result that the filter may be manufactured cheaper than has previously been possible. A decided advantage is obtained by suipplying the output circuit of the power ampli er with current from a filter independent from the filter supplyin the output of the other amplifier relay. en a single filter circuit is employed as in prior systems, the power amplifier draws such heavy current that it causes fluctuations 1n the potential supplied to the preceding amphfier. This is especially true when voice currents of low frequency are being received. The result is that the power amplifier reacts through the anode filter circuit and causes distortion and rumbling noises in the loud speaker. This difiiculty, however, is obviated by having separate filter circuits since filter circuit 57 for supplying the power amplifier cannot cause a potential drop to occur through a relatively high im edance choke 58 of the filter circuit 56. As filter 56 has more resistance than filter 57 the potential across conductors 206 and 207 is considerably less than that across conductors 206 and 209. The positioning of resistances 53 and 54 at a point in the rectifier circuit preceding certain of the filter elements also mmimizes the reaction on the grid bias voltage caused by a large incrgase in the plate current of the amplifier tu e.

In Fig. 3 there has been shown a B and C battery eliminator suitable for use with the ordinary radio receivin apparatus and which incorporates certain features of the system described above. In this arrangement the secondary 84 of the transformer 86 is connected to the rectifier element 87. The filaments of these elements are energized from another secondary winding 88.- The central tap 89 of secondary winding 84 is connected to the negative plate current conductor 91 through series resistances 92 and 93. The positive plate current conductor 94 is connected to the intermediate point of transformer winding 88. The conductor 96 serves as a positive late current connection for a power amplifi dr while conductors 97, 98 and 99, together with conductor 94, serve as sources of difierent plate current oten tials for preceding electron relays. Tie filter circuit for the power amplifier includes an inductive choke 115 and shunt capacitance 116, while the other filter includes an inductive choke 117 and capacitance 118. Capacitance 119 may be inc uded in both filter circuits. For supplyin reduced potentials to conductors 97, 98 an 99, the conductors 91 and 94 are shunted by an inductive impedance or resistance 120 which is shown as tapped for connections with the conductors 97 and 98. Conductors 91 and 97 may also be shunted by capacitance 121 and conductors 91 and 98 likewise shunted by capacitance 122, in order to minimize interaction between the relays and to further minimize alternating current ripples. Conductor 99 which forms a connection for the plate circuit of the detector, is shown as connected to the intermediate point between the resistance 123 and capacitance 124 which are connected in series and across conductors 91' and 94. The conductor 126 for supplying the grid bias potential for the power amplifier is connected to that end of resistances 92 and 93 which is adjacent to the source of rectified current. Another grid bias conductor 127 is provided for other amplifier relays and is connected between resistances 92 and 93. A

shunt capacitance 128 may also be provided to minimize ripples in the negative grid bias. These resistances may be re laced, if desired, by choke coils of suitabl; characteristics which are made use of as a part of the filter circuit.

In Fig. 4 there is shown a B batte eliminator utilizing the field coil of a lou speaker as one element of the filter circuits. Thus instead of utilizing the choke 118 as in the system of Fi 3, there is substituted the field coil 131 of t e loud speaker. If the inductance of coil 131 together with shunt capacitance 132 is not sufiicient to minimize all the ripples, a suitable voltage limiting device such as indicated at 133 may be connected across conductors 91 and 94. The exciting 0011 134 of the loud speaker is of course conniaced in the output circuit of the power amp 1 er.

I claim:

1. In a signaling system, a plurality. of electronic relays connected together in cascade and comprising a hi h frequency amplifier, a detector and a low requency amplifier, the low frequency amplifier relay having a grid and plate associated with its input and output clrcuits; a source of rectified alternating current for energizing said high frequency amplifiers and said output circuit, filter means for minimizing fluctuations in the current supplied from said source, said filter means including reactive elements, an impedance having resistance and ca acity in series and a separate'resistance in s unt with the negative lead from said source between some of the filter elements and said source, and a connection between said input circuit and the end of said impedance adjacent said source whereby the grid of said low frequency amplifier is rendered negative.

2. In an amplifying system, an electron relay having grid, plate and electron emission elements, an output circuit connected across the plate and electron emission element, an input circuit connected to the grid, a source of direct current for energizing the plate circuit, and a pair of impedance circuits, one including resistance and capacity in series and the other including resistance in shunt therewith connected to efiect a potential drop in the negative lead from said song-cc for placing a negative bias upon the g 3. In an amplifying system, an electron relay having grid, plate and electron emission elements, an output circuit connected across the plate and electron emission element, an input circuit connected to the grid, a source of direct current for energizing the plate circuit, a filter circuit inserted between the source and the output circuit, an im edance in series with the negative lead rom said source for effecting a potential drop, said impedance forming a part of the filter circuit and comprising a pair of resistors connected in parallel through a condenser, and means for impressing said potential drop upon the grid to bias the grid negatively with respect to the electron emission elemnt.

In testimony whereof, I have hereunto set In hand.

y GEORGE T ROYDEN. 

